The Evolution of the Sciences 



of this transformation presents a great analogy 

 with the segmentation of the germinal disc in 

 an incubated egg; it therefore helps us to 

 understand what takes place in this trans- 

 formation, one of the most mysterious in life. 

 The high temperature of the egg produces an 

 evaporation which concentrates the superficial 

 parts and determines diffusion currents, which 

 cause the segmentation of the mass. 



But the most suggestive of M. Leduc's 

 experiments appears to be the reproduction of 

 the phenomena of karyokinesis, that is to say, 

 the strange and complicated process by which 

 the cleavage of cells is brought about. Two 

 small globules situated close to the nucleus and 

 called attraction spheres become separated, 

 travel to the extremities of the cell and throw 

 on+ radiating fibres. At the same time the 

 chromatin filament, a long thread coiled up in 

 the nucleus, splits into lengths which form a 

 star at the centre of the cell, then each of these 

 lengths divides and the fragments execute 

 regular evolutions like a ballet figure in the 

 protoplasmic mass. Finally a partition separ- 

 ates the cell into two cells, in each of which 



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